When does building a house's wall shell in a factory beat building it on site?

What it found

Splits the exterior walls of the house-framing house into panels, nests the sheathing, loads the trailers and runs a Monte Carlo of the shell crew's days with weather. Panelised took 2.17 calendar days against 1.96 on site and cost 38% more at assumed rates; factory productivity does not change the days because the factory runs behind the foundation, and panelised is faster only from about 58 ft long (78 with no weather, 44 at 30% loss). Factory nesting saved 1 sheet in 33 (bound 26): a 97 in wall on a 108 in sheet wastes the same strip either way. A closed-panel variant (wrap, insulation, wiring and window setting built in the factory) flips the cost result: at a factory labour ratio of 0.45 or better panelising is within 1% of site cost and 0.3 beats it by 10%, and it saves about a day (2.16 against 3.18 d with weather); at 0.6 it still costs 12% more. Stylised: wall shell only, every labour rate and price is my assumption.

A figure from its own output

Paper, code and results

• README and method
• Experiments and results
• Code
• Tests

More in Open-source residential construction

• Which foundation is cheapest for a small house as the frost line gets deeper?Which foundation is cheapest for a small house as the frost line deepens? At 48 in frost a frost-protected shallow foundation is $13.2k against $20.6k slab, $24.1k crawlspace and $54.9k basement in a stylised model.
• Does a factory-built shell pay once the interest on the days it saves is counted?Does a factory-built shell pay once the interest on the days it saves is counted? Alone it saves 15.5 working days (0.22% of price) and breaks even near a $629,000 house at an assumed $1,500 crane day.
• How much do fewer handoffs, parallel trades, early ordering and a factory shell cut the time to build a house?How much do fewer handoffs, parallel trades, early ordering and a factory shell cut a house's build time? Discrete-event Monte Carlo: critical path 100 working days, baseline 214; early ordering -63 d, fewer handoffs -21, a factory shell only -6 unless ordered at day 0 (-78). Stylised, uncalibrated.
• Does an independent second schedule model agree with house-schedule on what shortens a house build?Does an independent second schedule model agree with house-schedule? Same ranking (early ordering of long-lead items first, prefab only with it, handoff gap matters), different magnitudes (-11% against -29%): sizes are set by assumptions. Crew-merging does nothing. Every input assumed.
• Does the month a house build starts change how long it takes and the interest paid?Does the month a house build starts change how long it takes? Same Monte Carlo as house-schedule with a monthly weather calendar: in an assumed cold climate a December start takes 231 working days against 211 for July (~20 d); in a mild one, 4 d. Early ordering saves ~63 d in every month. Weather numbers assumed.
• Does solar gain through windows change which envelope is cheapest over 30 years, and is the direction the windows face worth money?Does solar gain through windows change the cheapest envelope, and is window orientation worth money? Adds first-principles solar geometry to house-energy: U 0.50 stays optimal in 15 of 16 cases, and orientation is worth $420–$1,740 of 30-year cost. Stylised: degree-day model, assumed prices and clearness, not EnergyPlus.

All 41 Open-source residential construction projects →

Other research topics

Proper scoring & elicitation28Effort & peer prediction9Verification games & slashing19Detection & tolerances14Markets as routers13Prediction-market design9Paying contributors8Decentralised training systems23Digital twins & sim-to-real164LLM chip design loops40Robot manufacturing loops53Ambient AI assistant46Self-replicating manufacturing34Simulation-first design64Engineered clothing45Task-specific AI accelerators40Algorithmic chip-design loops42Open-source purpose-built robots44The software-engineering loop43Adversarial human imitation41Open-source residential construction41Autonomous multi-angle capture34Sensing, imaging and 3D31Energy supply and dense energy storage39Robot societies among people31Agentic co-design of low-cost robots27Laundry-hanging robots25Machine learning on qualitative data23Robots on the building site27Civilizations & group psychology1History & human sciences1

Produced with AI assistance (Claude). Results are from the code in this repository and are simulated or stylised unless the abstract says otherwise; nothing here implies affiliation with or endorsement by any lab, researcher or company cited. MIT licensed.